A pantograph is nice for tracing an outline quickly, but it might be more than you need. If you want to greatly enlarge a pattern, the grid method is the way to go: You draw a small grid across your small image, a big grid across your big surface, and copy the shape you see in each small square to the corresponding big square.
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You want a pantographhttp://www.daube.ch/docu/glossary/drawingtools.html#pantographYou put a pen in one side, and a stylus in the other (depending on if you want to scale up or down.they're cheap to buy, and cheaper to make (out of a few paint stir sticks and bolts)
see attached image for the deadly easy version using cardboard and tacks.